The present invention relates to a process system for transferring and processing a substrate such as a semiconductor substrate or an LCD substrate.
In the photolithographic step of a semiconductor device manufacturing process, a resist coating process and a developing process are performed. In the resist coating process, a resist film is formed on a surface of a semiconductor wafer (hereinafter, referred to as "wafer"). In the development process, the wafer is developed after the resist-coated wafer is exposed to light. Hitherto, the resist coating process and the developing process have been performed at the corresponding process units assembled in one process system, namely, a complex process system, in accordance with a predetermined sequence, as known in, for example, Jpn. Pat. Appln. KOKOKU publication No. 2-30194.
One example of such a complex process system is shown in FIG. 1. In the resist coating/developing process system 101, the following units are incorporated together: a cassette station 102 for loading/unloading a wafer W into/from a cassette, a brush washing unit 103 for washing the wafer W with a brush, a jet-water washing unit 104 for washing the wafer W with high-pressure jet water 104, an adhesion unit 105 for rendering the surface of the wafer W hydrophobic in order to increase resist-deposition, a cooling unit 106 for cooling the wafer W to a predetermined temperature, a resist coating unit 107 for coating a resist solution on the surface of the wafer W. a heating unit 108 for heating the wafer W before and after the resist coating, a periphery light-exposure unit 109 for removing the resist from the periphery of the wafer W, a wafer-transferring stage 110 for transferring the wafer W to an adjacent light-exposure unit (not shown), and a developing unit 111 for immersing the light-exposed wafer W in a developing solution to dissolve an irradiated potion or a non-irradiated portion, selectively.
In the center of the resist coating/developing process system 101, a corridor-form wafer transfer path 112 is provided in the longitudinal direction (Y-direction). Individual process units are provided with a front face (having a load/unload port) directed to the wafer transfer path 112. The wafer W to be processed is held by a holding member 114 of the wafer transfer apparatus 113, which is movable along the wafer transfer path 112, and then transferred and delivered between the individual units.
The wafer W heated by the heating unit 108 is transferred from the heating unit 108 to the cooling unit 106 by means of the wafer transfer apparatus 113. At the cooling unit 106, the wafer W is cooled to a predetermined temperature and then transferred to the periphery light-exposure unit 109 and the cassette station 102. To describe more specifically, the wafer W applied with a resist solution in the resist coating unit 107 is held by the holding member 114 of the wafer transfer apparatus 113 and unloaded from the unit 107, and then, transferred to the heating unit 108. The wafer W is heated to, for example, 100.degree. C. and unloaded from the unit 108 by the holding member 114 of the wafer transfer apparatus 113, and then, transferred again to the cooling unit 106. In the cooling unit 106, the wafer W is cooled to, for example, 23.degree. C. and transferred to the periphery light-exposure unit 109 by means of the wafer transfer apparatus 113. After development of the wafer W is completed at the developing unit 111, the wafer W is unloaded from the unit 111 by the holding member 114 of the wafer transfer apparatus 113 and transferred to the heating unit 108. The wafer W is heated to, for example, 100.degree. C. The wafer W is then unloaded therefrom by the holding member 114 of the wafer transfer apparatus 113 and transferred to the cooling unit 106. After the wafer W is cooled to, for example, 23.degree. C., the wafer W is transferred to the cassette station 102 by means of the wafer transfer apparatus 113.
However, particularly in a complex process system incorporating various process units together in one place, the wafers W requiring the cooling process assemble at the cooling unit 106 and wait for subjection to the process. In an attempt to avoid this waiting, it is considered possible that the wafers W waiting for the cooling process remain held by the holding member 114 of the wafer transfer apparatus 113. However, since the wafer transfer apparatus 113 must transfer a number of wafers one by one, if the wafer transfer apparatus 113 keeps holding the wafer W as mentioned above, the movement of the apparatus 113 will stop. As a result, the throughput will decrease. Another possibility is that the wafer W waiting for the cooling process is kept in the heating unit 108. However, the excessively long heating time produces adverse effects on the thickness and hardness of the resist film and increases the cooling time.
There is a further possibility that the problem of the number of wafers W waiting for the cooling process is overcome by increasing the number of cooling units 106. However, space is required for those units. Since such a system is usually disposed in a clean room, the increase of space results in a cost increase, producing a significant problem.